False Info About False Positives for Colon Cancer

The results of a recent study may change the way you're asked to prepare for a fecal occult blood test (FOBT). Researchers from Indiana University Medical Center found that the regular use of aspirin or NSAID's (non-steroidal anti-inflammatory drugs, like ibuprofen) does not cause false positives on fecal occult blood tests. (Please click on the headline above to link to the full story.)

Just How Prevalent Are False Positives?

According to an article entitled “The Economic Impact of False-Positive Cancer Screens,” published in Cancer Epidemiology Biomarkers & Prevention in December 2004, of “1,087 prostate, lung, colorectal, and ovarian cancer screening trial participants enrolled in a large managed care organization ... 43% of the study sample incurred at least one false-positive cancer screen.”

This is not to say that periodic cancer scans should not be performed. On the contrary, they are essential to the early detection of cancer. However, the danger arises when a physician insists on a definitive course of action involving potentially dangerous medication, unnecessary and harmful treatments, or surgery on the basis of a single test without alerting the patient to the potential for a false positive.

The False-Positive "Necklace"

A woman with papillary thyroid carcinoma treated with surgery and postoperative 131-I returned four years later for a whole-body survey. The imaging results initially suggested disease recurrence but were later found to be false positive and due to 131-I uptake in a necklace that had been contaminated by the patient’s saliva. According to doctors at the University of Washington in Seattle, where this occured, this case stresses the importance of having the patient remove all jewelry before undergoing a radioiodine survey.

Early Detection of Lung Cancer

Lung cancer kills more people worldwide than any other cancer. However, according to a report published in The Journal of Best Clinical Practices for Today's Physician, no available lung cancer screening protocol has proven sufficiently robust, safe, and cost effective to warrant a recommendation for population-based screening. The U.S. Preventive Services Task Force stated that although it found "fair evidence that screening with low-dose computerized tomography, chest x-ray, or sputum cytology can detect lung cancer at an earlier stage" than it would be detected without screening, the group also found "poor evidence that any screening strategy for lung cancer decreases mortality."

Furthermore, the risks inherent in the high number of false-positive test results that may occur from the use of these screening tools are cause for concern. These risks include the need for invasive diagnostic procedures to characterize suspicious nodules as benign or malignant and the potential anxiety caused by a false-positive result. Thus, although low-dose spiral CT offers a proven method for detecting small (less than 1 cm) lung tumors that are at an early, highly resectable stage, the challenge lies in developing diagnostic algorithms that minimize the number of false-positive results and limit the number of patients who undergo biopsy without missing treatable cancers.

Saying No Is a Patient's Choice

Over the last several years, researchers have begun to study how patients balance the risks and benefits of proposed interventions. To read the full article, published in The New York Times, click on the headline above.

False-Positive Mammograms Vary Among Radiologists

A woman's chance of getting a false-positive result on a screening mammogram depends a lot on the radiologist interpreting the image, according to a study published in the Journal of the National Cancer Institute.

Among the 24 radiologists interpreting the X-ray films, some produced false positives as seldom as about once for every 29 mammograms (3.5%) while others reported a false positive for every 13 mammograms (7.9%). Radiologists more recently out of medical school, with less mammography-reading experience, had two-to four-times the false-positive rates of older, more experienced radiologists.

So what can you do? The American Cancer Society advises that women return to the same mammography facility every year since radiologists will have their earlier mammogram films for comparison. And premenopausal women may wish to have mammograms when they are not menstruating, since there is some evidence to indicate that the increase in breast density during menstruation slightly reduces accuracy.

How Accurate Is a CA-125 Test for Detecting Ovarian Cancer?

According to Johns Hopkins Pathology, the CA-125 test should not be used alone to detect ovarian cancer. Instead it should be used in conjuction with transvaginal sonography and rectovaginal pelvic examination for greater accuracy since combining detection methods lowers the number of false positive results.

The CA-125 test only returns a true positive result for about 50% of Stage I ovarian cancer patients and has an 80% chance of returning true positive results from stage II, III, and IV ovarian cancer patients.

Second Opinions

Respected cancer physician Jerome Groopman, M.D., discussed the convergence of illness and spirituality in his first book, The Measure of Our Days. In Second Opinions: Stories of Intuition and Choice in the Changing World of Medicine, he shifts his focus to the ways intuition informs his medical decisions and enhances the quality of his patient relationships (even giving him an edge when examining a patient on referral). In eight chapters that vividly recount cases whose outcomes hinge as much on the doctor's gut feeling and empathy as on his expertise, Groopman eschews the impersonal and know-it-all role of the doctor, describing instead dire cases in which careful consideration of both the emotional and medical issues positively impacted his approach to treatment.